I’d want to say something supportive too. But when I’ve done that, almost every time, the response isn’t human warmth. People in these jobs are very practiced in maintaining professional courtesy. She might appreciate your kindness, but you’re unlikely to see it.
What I’ve taken to doing instead are any of: a) simply making eye contact and saying Thank You; b) saying that I’d like to submit a written compliment, and asking what I can do (it’s usually a feedback slip); c) asking for a way of complaining about the other passenger (usually the same feedback form).
In short, there are channels for this sort of thing. They are meaningful and are there to be used.
Politeness matters, as has been set out in various stories, recent or not-so….